The present invention relates to a method of producing an optical waveguide material (optical fiber) which is very low in light attenuation.
There is known a rod-in-tube method as a typical method of producing an optical waveguide material, which comprises inserting a silica glass rod (a core material) into a silica glass tube (a cladding material), fusing the core material and the cladding material by heating and pulling the fused core material and cladding material.
This method, however, has the defect that the optical fiber thus produced is high in light attenuation, because the boundary formed by the fusion of the core material and the cladding material is apt to be contaminated with airfoams and impurities.
In order to resolve this defect, prior to the insertion of the core material into the cladding material, these two materials were respectively mechanically or chemically polished or heat-treated to purify the surfaces thereof, for example, in a germ-free room, but the fact was that as the core material and the cladding material thus treated were again exposed to the air in the subsequent handing, reattachment of impurities to the surfaces of these two materials could not be avoided.